I. Field of the Invention
This invention relates to a semiconductor integrated circuit using dielectrical material to electrically isolate circuit components, and a method for manufacturing the same.
II. Description of the Prior Art
It is well-known to use the selective oxidation technique (S.O.T.) for isolating circuit components. In S.O.T., silicon nitride film is employed as a mask layer to prevent oxidation of a silicon substrate. Circuit components as transistors, diodes and resistors are formed in active regions of the silicon substrate which had been covered by the silicon nitride film. The circuit components are surrounded by a silicon oxide layer (field oxide layer).
However, in an integrated circuit manufactured by S.O.T., the field oxide layer extends to a portion of the substrate where the active region is to be formed. For example, if a field oxide layer of 1 .mu.m thickness is formed using a silicon nitride layer and silicon oxide layer as masking layers, the field oxide layer extends 0.7 .mu.m into the portion where the active region is to be formed. Accordingly, in case that the designed width of the active region is A.sub.1 and the actual width is A.sub.2, the difference (A.sub.1 -A.sub.2) is about 1.4 .mu.m. Therefore at least 1.4 .mu.m of the width of the supposedly active region is unusable. This reduces the integration density.